Display drive circuit including an output terminal

ABSTRACT

A display drive circuit formed in a chip manufactured by a chip on glass implementation, which is connected to lead lines formed on a glass substrate, includes a rectangularly-shaped substrate, a power supply line formed on the substrate, the line being elongated along the longer side of the rectangular shaped substrate, a plurality of output terminals formed on the rectangular shaped substrate, the output terminal being disposed along the power supply line, a plurality of bump electrodes, each of which connects one of the output terminal to one of the lead lines, switches disposed along the power supply line, each of which is connected between the one of the output terminals and the power supply line, a single power supply terminal, which is disposed near the middle of the power supply line, being connected to the power supply line.

CROSS-REFERENCE TO RELATED APPLICATION

This is the continuation of U.S. application Ser. No. 14/190,495, filedon Feb. 26, 2014, and was allowed on Jul. 31, 2015, which was adivisional of U.S. application Ser. No. 11/907,200, filed on Oct. 10,2007, now abandoned, the subject matters of which are incorporatedherein by reference. These prior US applications and the presentcontinuation application claim the benefit of priority of JapanesePatent Application No. 2006-337902, filed Dec. 15, 2006, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a display drive circuit for operating a displaydevice, which uses an organic electroluminescent device (hereinaftercalled “an organic EL device”) or a light emitting diode (hereinaftercalled “an LED”), and specifically, relates to a display drive circuitformed in a chip manufactured by a Chip On Glass (hereinafter called “aCOG”) implementation technology, which connects lead lines for a displayformed on a glass substrate by bonding.

2. Description of the Related Art

FIG. 2A is a diagram showing the entire skeleton framework of a displaypanel having an organic EL drive circuit formed on a COG, and FIG. 2B isa sectional view taken on line I1-I2 of FIG. 2A.

The display panel includes a nearly square-shaped glass substrate 2, anda display area 10 displaying the images is located in the center of thesubstrate 2. In the display area 10, a plurality of data lines SEG and aplurality of scanning lines COM, which are perpendicular to the datalines SEG, are formed. An organic EL device 11 is formed at eachintersection of the data lines SEG and the scanning lines COM so thatthe organic EL devices 11 are arranged in a lattice-like manner. Both ofthe data lines SEG and the scanning lines COM extend from the displayarea 10 to an edge of the glass substrate 2 as lead lines. Each of thedata lines SEG and the scanning lines COM are formed of a transparentconductive layer using ITO (indium Tin Oxide) for instance. Thetransparent conductive layer using ITO has a large wiring resistance,compared to that in a wiring layer made of cupper.

A display drive circuit according to the related art includes aplurality of data line drive circuits 20-1 . . . 20-n and a plurality ofscanning line drive circuit 30-1 . . . 30-n. Each of the data line drivecircuits 20-1 . . . 20-n is formed on one of the lead lines of the datalines SEG extending from the display area 10, and is formed in anindividual chip, which is implemented by the COG method. Each data linedrive circuit 20 includes switching elements such as transistors, whichare operated in response to image data for displaying the images, andwhich have a function to supply a predetermined electric current to eachof the data lines SEG. Also provided on each of the lead lines of thescanning lines COM extending from the display area 10 is a respectiveone of the scanning line drive circuits 30-1 . . . 30-n, each formed inan individual chip, which is implemented by the COG method. Eachscanning line drive circuit 30 includes switching elements such astransistors, which are operated in response to image data for displayingthe images, and which have a function for supplying ground electricpotential (ex. 0 volt) to the scanning lines SEG.

The glass substrate is equipped with unillustrated electricalcomponents, such as a control circuit, in an area around the displayarea 10.

FIG. 3 is a skeletal circuit diagram in an area X of the FIG. 2A, whichis adjacent to one of the organic EL devices 11, and in an area Y of theFIG. 2A, which is a part of one of the scanning line drive circuit 30.FIG. 4A is a diagram showing a skeleton framework of one of the scanningline drive circuit 30 shown in FIG. 2A, and FIG. 4B is a sectional viewtaken on line I21-I22 of FIG. 4A.

As shown in FIG. 2A, the organic EL device is connected in a forwarddirection between a data line SEG and a scanning line COM that isperpendicular to the data line in the area X.

As shown in FIGS. 2A and. 2B and FIGS. 4A and 4B, each of the scanningline drive circuit 30 includes a rectangularly-shaped substrate 31. Anelongated ground line 32 having a width W and length L is formed on thesubstrate 31 along the longer side of the substrate 31. A plurality ofoutput terminals 33-1 . . . 33-n are disposed on the substrate 31 alongone of the longer side of the substrate 31, and a plurality of aswitches 34-1 . . . 34-n, each of which includes a transistor, areformed on the substrate 31 wherein each of the switches 34 is disposedbetween one of the output terminals 33-1 . . . 33-n and the ground line32. The switches 34 are operated by the control circuit.

At both ends of the ground line 32, two ground terminals 35-1 and 35-2are formed near the opposite longer side of the substrate 31. Eachoutput terminal 33 is connected to one of the scanning lines through abump electrode 36 formed thereon, and each of the two ground terminalsis grounded through another bump electrode 36 formed thereon.

One of the organic EL devices 11 (for example the organic EL device 11illustrated in FIG. 2A) emits light in the following way. Initially, thescanning line drive circuit 30-1, which connects the organic EL device11 to be eliminated, is connected to the ground line 32 through theoutput terminal 33-1 and the switch 34-1 so that the ground electricpotential (0 volt) is supplied to the scanning line COM connected to theorganic EL devices 11. Then, the drive current from the data line drivecircuit 20-1 is supplied to the data line SEG, which is connected to theorganic EL devices 11. Then, the drive current flows in the flowingorder; the data line SEG→the organic EL device 11→the scanning lineCOM→the output terminal 33-1→switch 34-1→the ground line 32→the groundterminals 34-1 and 34-2. As a result of the flow of the drive current asdescribed above, the organic EL device 11 emits light. The lightintensity of the organic EL device 11 depends on the value of the drivecurrent.

Some technologies relating to the display panel having a configurationsimilar to that described above are disclosed in the followingpublications.

Reference 1: Japanese laid open patent 2002-151276

Reference 2: Japanese laid open patent 2003-131617

Reference 3: Japanese laid open patent 2004-206056

Reference 4: Japanese laid open patent 2005-144685

According to the reference 1, an EL display device with a good balancebetween colors of EL elements and with a good balance in emissionintensity, which is capable of displaying brightly hued images, isdisclosed. According to the reference 2, EL drive circuits, which aresimilar to the drive circuits of FIGS. 2A, 2B and 3, are disclosed.According to the reference 3, EL drive circuits, which suppressluminance unevenness and retain display quality without enlarging aframe part, are disclosed. Further, the reference 4 discloses line headsof the configuration without any difference in the quantity of lightemitted from a plurality of light emitting elements, and an imageforming apparatus using the same.

The following problems are recognized in the display drive circuit, forexample, the scanning line drive circuits 30, in the related art.

In such a scanning line drive circuits 30, as described above, twoground terminals 34-1 and 34-2 are connected respectively to theopposite ends of the ground line 32, and each ground terminal 34-1 or34-2, which are implemented by the COG method, is grounded through arespective one of the bump electrodes 36.

Under the COG implementation, not only is high contact resistancecreated, but also its deterioration is severe. With consideration of thedeterioration, the value of the contact resistance varies greatly, suchas from few Ω to few tens Ω. The resistance value of the ground line 32in the scanning line drive circuits 30 is determined by the amount of anelectromigration. Thus, in the case that an active matrix organic ELdisplay panel as shown in FIGS. 4A and 4B is driven, it is assumed thatthe maximum allowable current is required to be 1.0 A of direct current.Here, the electromigration is the phenomenon that occurs when some ofthe momentum of moving electrons is transferred to nearby-activatedions. This causes the ions to move from their original position.

In the case of the assumption described above, since the maximumallowable current is generally set at 1 mA, the width W of the groundline 32 is required to be a 1000 m when the length L of the ground line32 is set to be a 10,000 m. Since a sheet resistance is 0.05 Ω/□, theresistance value of the ground line 32 having the length L is calculatedto be 0.5Ω. As a result, as shown as an arrow in FIG. 4A, the outputelectric current, which is supplied from the left-end output terminal33-1 to the ground line 32 through the switch 34-1, may flow to groundthrough the right-end ground terminal 35-2 in the case that the contactresistance at the ground terminal 35-1 is to be greater than the sum ofthe resistance value of the ground line 32 and the contact resistance atthe ground terminal 35-2.

Further, the dispersion of the contact resistance can be reduced by thesize of the ground terminal 35-1 or 35-2. However, if the sizes of theboth ground terminals 35-1 and 35-2 are reduced, it would be required toform a hundred ground terminals near each ground terminal 35-1 and 35-2to obtain the capacity to pass the electric current to ground. As aresult, the size of the substrate 31 becomes larger because its longerside is further elongated. This is a distant idea in view of thedifficulty of its implementation. Further, the width W of the groundline 32 may need to be a 1000 m so that the shorter side of thesubstrate 31 is also elongated. As a result, the total side of thescanning line drive circuit becomes larger. This is a specific problemwith implementation using the COG method.

This problem cannot be solved by the technology disclosed in theabove-described references. For example, according to FIG. 1 of thereference 1, the width of the wiring (107), which connects the twoterminals (105) acting as the supply terminals to the current supplylines (104), is set to be a best value wherein two terminals (105)correspond to the ground terminals 35-1 and 35-2 and the current supplylines (104) correspond to the dale lines SEG and the wirings (107)correspond to the ground line 32. If the width W of the ground line 32is set at the best value by using the technology disclosed in thereference 1, the ground line 32 having a 1000 m width is required asdescribed above. Thus, the shorter side of the substrate 31 is elongatedso that the problem is not solved.

According to the reference 3, the width of the power supply linesupplying the power supply to the EL display panel is reduced to half sothat the area of the flame part can be reduced wherein the area of theflame part corresponds to the area around the display area 10 shown inFIG. 2A. The reason that the width of the power supply line is reducedto half be that the power supply line extends from the mounting terminalarea (102) at both of its sides, as shown in FIG. 4 of the reference 3.The technology disclosed in the reference 3 corresponds to thedescription above in that the width W of the ground line 32 is reducedto half by using two ground terminals 35-1 and 35-2 connected at theboth ends of the ground line 32, as shown in FIG. 4A. Thus, the problemis not solved.

The reference 4 does not consider any width of the wiring, and the COGtechnology is not used. Thus, the teachings of reference 4 cannot becombined with the related arts to solve the problem.

As described above, the problem particularly occurring in the COGtechnology cannot be solved by the technology disclosed in theabove-described references.

SUMMARY OF THE INVENTION

An objective of the invention is to solve the above-described problemand to provide a display drive circuit, whose operation does not dependon the variety of the contact resistance value without making itssubstrate larger.

The objective is achieved by a display drive circuit formed in a chipmanufactured by a chip on glass implementation, which is connected tolead lines formed on a glass substrate, comprising, arectangularly-shaped substrate, a power supply line formed on thesubstrate, the line being elongated along the longer side of therectangularly-shaped substrate, a plurality of output terminals formedon the rectangularly-shaped substrate, the output terminal beingdisposed along the power supply line, a plurality of bump electrodes,each of which connects one of the output terminal to one of the leadlines, switches disposed along the power supply line, each of which isconnected between the one of the output terminals and the power supplyline, a single power supply terminal, which is disposed near the middleof the power supply line, being connected to the power supply line.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more particularly described with reference to theaccompanying drawings, in which:

FIG. 1A is a plan view showing a skeleton framework of a display drivecircuit, such as a scanning line drive circuit, used in a display panel,according to a first embodiment;

FIG. 1B is a sectional view taken on line I21-I22 of FIG. 1A;

FIG. 2A is an entire plan view of a configuration diagram showing askeleton framework of a display panel having an organic EL drive circuitformed on a COG;

FIG. 2B is a sectional view taken on line I1-I2 of FIG. 2A;

FIG. 3 is a skeletal circuit diagram in an area X of the FIG. 2, whichis adjacent to one of the organic EL devices 11 and in an area Y of theFIG. 2, which is a part of one of the scanning line drive circuit 30;

FIG. 4A is a plan view of a configuration diagram showing a skeletonframework of one of the scanning line drive circuit 30 shown in FIG. 2;

FIG. 4B is a sectional view taken on line I21-I22 of FIG. 4A;

FIG. 5A is a plan view showing a skeleton framework of a display drivecircuit, such as a scanning line drive circuit, used in a display panel,according to a second embodiment;

FIG. 5B is a sectional view taken on line I31-I32 of FIG. 5A;

FIG. 6 is an enlarged view showing a layout of the scanning line drivecircuit of FIG. 5A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiment of the invention is explained with reference todrawings as follows. In each drawing, the same reference numbersdesignate the same or similar components.

First Embodiment

FIG. 1A is a plan view showing a skeleton framework of a display drivecircuit, such as a scanning line drive circuit, used in a display panel,according to a first embodiment and FIG. 1B is a sectional view taken online I21-I22 of FIG. 1A.

As well as the display panel shown in FIGS. 2A and 2B, the display panel40 includes a nearly square-shaped glass substrate 41, and a displayarea 50 displaying the images is formed in the center of the substrate41. In the display area 50, a plurality of data lines SEG and aplurality of scanning lines COM, which are perpendicular to the datalines SEG, are formed. An organic EL device 51 is formed at eachintersection of the data lines SEG and the scanning lines COM so thatthe organic EL devices 51 are arranged in a lattice-like manner. Both ofthe data lines SEG and the scanning lines COM extend from the displayarea 50 to an edge of the glass substrate 41 as lead lines. Each of thedata lines SEG and the scanning lines COM are formed of a transparentconductive layer using ITO (indium Tin Oxide) for instance. Thetransparent conductive layer using ITO has large wiring resistance.

A display drive circuit includes a plurality of data line drive circuits70 and a plurality of scanning line drive circuits 60. Each of the dataline drive circuits 70 is formed on one of the lead lines of the datalines SEG extending from the display area 50, and is formed in anindividual chip, which is implemented by the COG method. Each data linedrive circuit 70 includes switching elements such as transistors, whichare operated in response to image data for displaying the images, andwhich have a function to supply a predetermined electric current to eachof the data lines SEG. Also provided on each of the lead lines of thescanning lines COM extending from the display area 50 is a respectiveone the scanning line drive circuits 60 formed in an individual chip,which is implemented by the COG method. Each scanning line drive circuit60 includes switching elements such as transistors, which are operatedin response to image data for displaying the images, and which have afunction for supplying ground electric potential (ex. 0 volt) to thescanning lines SEG.

Each of the scanning line drive circuit 30 includes arectangularly-shaped substrate 61. An elongated ground line 62 having apredetermined width W and a predetermined length L (ex. 10000 m), andhaving a resistance value R (ex. 0.5Ω) is extended from one of theshorter side of the substrate 61 to the opposite side on the substrate61 along one of the longer side of the substrate 61. A plurality ofoutput terminals 63-1 . . . 63-n are disposed regularly on the substrate31 along another longer side of the substrate 31, and a plurality of aswitches 64-1 . . . 64-n, each of which includes a transistor, areformed on the substrate 61 wherein each of the switches 34 is disposedbetween one of the output terminals 63-1 . . . 33-n and the ground line62. The switches 34 are operated by an unillustrated control circuitdisposed in an area around the display area 50.

A single ground terminals 65 is disposed near the middle location of theanother longer side of the substrate 61 between another longer side ofthe substrate 61 and the ground line 62, and is connected to the groundline near its middle location. Thus, the resistance value of the groundline 62 between the ground terminals 65 and the left end of the groundline 62 is R/2 (about 0.25Ω), and the resistance value of the groundline 62 between the ground terminals 65 and the right end of the groundline 62 is also R/2 (about 0.25Ω). Each output terminal 63 are connectedto one of the scanning lines COM through an AU bump electrode 66 formedthereon, and the ground terminals 65 are grounded through another AUbump electrode 66 formed thereon.

The operation of the display drive circuit of the first embodiment isexplained below.

One of the organic EL devices 51 (for example the organic EL devices 51illustrated in FIG. 1A) emits light in the following way. Initially, thescanning line drive circuit 60, which connects the organic EL device 51to be eliminated, is connected to the ground line 62 through the outputterminal 63-1 and the switch 64-1 so that the ground electric potential(0 volt) is supplied to the scanning line COM connected to the organicEL devices 51. Then, the drive current from the data line drive circuit70 is supplied to the data line SEG, which is connected to the organicEL devices 51. Then, the drive current flows in the flowing order; thedata line SEG→the organic EL device 51→the scanning line COM→the outputterminal 63-1→switch 64-1→the ground line 64→the single ground terminals65. As a result of the flow of the drive current described above, theorganic EL device 51 emits light. The light intensity of the organic ELdevice 51 depends on the value of the drive current.

In the case that the switches 64-1 . . . 64-n are turned on by thecontrol circuit in series from the left (64-1) to the right (64-n)illustrated in the FIG. 1A, the drive current from the output terminals63-1 . . . 63-n/2, which are located in the left side, are flowed to theground line 62 through the switches 64-1 . . . 64-n/2. Then the drivecurrent flows on the ground line 62 from the left to the center, andthen flows to the ground through the single ground terminal 65. On theother hand, the drive current output from the output terminals63-(n/2+1) . . . 62-n at the right side, flows to the ground line 62through the switches 64-(n/2+1) . . . 64-n respectively. Then the drivecurrent flows on the ground line 62 from the right to the center, andthen flows to the ground through the single ground terminal 65.

As described in the Background of the invention, as well as the scanningline drive circuit 30 shown in FIG. 4, since large contact resistance isformed on the COG implementation, when it is assumed that the maximumallowable current is required to be 1.0 A of direct current, the maximumallowable current is generally at 1 mA. Thus, under this assumption,when the width W of the ground line 62 is set to be a 1000 m and thelength L of the ground line 62 is set to be a 10,000 m, the resistancevalue of the ground line 32 having the length L is calculated 0.5Ω sincea sheet resistance is to be 0.05Ω/□.

However, according to the first embodiment of the invention, since theground terminal 65 is located near the middle of the ground line 62, andis connected to the ground line 62, the drive current, which flowsthrough the switches 64-1 . . . 64-n/2 located in the left side, flowson the ground line 62 from its left to its center, and then flows to theground through the single ground terminal 65 while the drive current,which flows through the switches 64-(n/2+1) . . . 64-n/2 located in theright side, flows on the ground line 62 from its right to its center,and then flows to the ground through the single ground terminal 65. Inother words, the route of the drive current flowing on the ground line62 does not depend on the dispersion of the contact resistance, and isalways the same. Again, in the scanning line drive circuit in therelated art shown in FIGS. 4A and 4B, the route of the drive currentflowing on the ground line 62 through the switch 34-1 depends on thecontact resistances of the ground terminal, which are determinedaccidentally in the COG process. In other words, in a certain occasion(if the contact resistance of the ground terminal 35-1 is smaller thanthe sum of the resistance values of the ground line 32 and the groundterminal 35-2), the drive current reached on the ground line 32 throughthe switch 34-1 flows to the ground through the ground terminal 35-1. Tothe contrary, in another certain occasion (if the contact resistance ofthe ground terminal 35-1 is greater than the sum of the resistancevalues of the ground line 32 and the ground terminal 35-2), the drivecurrent reached on the ground line 32 through the switch 34-1 flows tothe ground through the ground terminal 35-2. However, according to thefirst embodiment of the invention, the drive current reached on theground line 62 through the switch 64-1 always flows to the groundthrough the single ground terminal 65 so that the route of the drivecurrent from a certain switch is always the same. In the firstembodiment of the invention, the longest route on the ground line 62 ofthe drive current is the half of the length of the ground line 62 (L/2).Since the sheet resistance is to be 0.05Ω/□, the resistance value R ofthe ground line 32 having the length L/2 is calculated 0.25Ω. As aresult, even if the width W of the ground line 62 can be reduced tohalf, such as at a 500 mm, the electromigration may not occurs.Accordingly, the length of the substrate 61 can be shorter at itsshorter side, and the total size of the scanning line drive circuit 60can be miniaturized.

According to the first embodiment of the invention, at least thefollowing benefit can be expected. Since the single ground terminal 65is located near the middle of the ground line 62, and is connected tothe ground line 62, the length L of the ground line 62 is not changedwhile the width W of the ground line 62 is reduced to half. As a result,the length of the substrate 61 can be shorter at its shorter side, andthe total size of the scanning line drive circuit 60 can beminiaturized.

Second Embodiments

While a single ground terminal 65 is formed in the scanning line drivecircuit as shown in FIG. 1A in the first embodiment, a first group ofground terminals are formed near the middle of a ground line in ascanning line drive circuit, a second group of ground terminals areformed at one end of the ground line, and a third group of groundterminals are formed at the other end of the ground line. The secondembodiment is explained with reference to FIGS. 5A, 5B and 6.

When the scanning line drive circuits 60 are arranged near the displayarea 50, as well as the arrangement of the scanning line drive circuits30-1 . . . 30-n shown in FIG. 2, uniformity of displaying the images mayoccur because of a differences of the power supply impedance, which maybe occur between the scanning lines COM, each of which is connected toone adjacent scanning line drive circuits. For example, a differences ofthe power supply impedance may be occur between the scanning line COMdisposed at the most right in the most right side of the scanning linedrive circuit in the left and the scanning line COM disposed at the mostleft in the most left side of the scanning line drive circuit, which isnext right to aforementioned scanning line drive circuit, in the right.To eliminate the uniformity of displaying the images occurred at thescanning lines having a difference of the power supply impedance, thescanning line drive circuit according to the second embodiment iscomposed as follows

FIG. 5A is a plan view showing a skeleton framework of a display drivecircuit, such as a scanning line drive circuit, used in a display panel,and FIG. 5B is a sectional view taken on line I31-I32 of FIG. 5A. FIG. 6is an enlarged view showing a layout of the scanning line drive circuitof FIG. 5A. In each drawing and in the FIGS. 1A and 1B, the samereference numbers designate the same or similar components.

As shown in FIG. 5A, a first group of an even number (l) of groundterminals 65-1 is disposed near the middle of a ground line 62 in ascanning line drive circuit 60A, and each of the ground terminals 65-1of the first group is connected to the ground line 62. A second group ofa number (m) of ground terminals 65-2 is disposed at one end of theground line 62 in the scanning line drive circuit 60A, and each of theground terminals 65-2 of the second group is connected to the groundline 62. A third group of a number (n) of ground terminals 65-3 isdisposed at the other end of the ground line 62 in the scanning linedrive circuit 60A, and each of the ground terminals 65-2 of the secondgroup is connected to the ground line 62. The numbers (m) and (n) couldbe the same, or could be the different. Each of the ground terminals65-1, 65-2 and 65-2 in the first through third group is grounded throughan AU bump electrode 66 formed thereon. Generally, the planar dimensionof each ground terminals 65-1, 65-2 and 65-3 is the same.

The number (l) of the ground terminals 65-1 is set to be greater thanthat (m) of the ground terminals 65-2 or that (n) of the groundterminals 65-2. For this reason, a total of planar dimension of theground terminals 65-1 of the first group is set to be larger than atotal of planar dimension of the ground terminals 65-2 of the secondgroup or a total of planar dimension of the ground terminals 65-3 of thethird group. Thus, a sum of the contact resistance of the groundterminals 65-1 of the first group, each of which is connected inparallel, is smaller than that of the ground terminals 65-2, each ofwhich also is connected in parallel or that of the ground terminals65-3, each of which also is connected in parallel.

Furthermore, as shown in FIG. 6, each of pitches p1 between the groundterminals 65-1 of the first group is set to be greater than each ofpitches p2 between the ground terminals 65-2 of the second group or eachof the pitches p3 between the ground terminals 65-3 of the third group.The distances of the pitches (p2) and (p3) could be the same, or couldbe the different.

The operation of the display drive circuit 60A of the second embodimentis explained below. In the case that the switches 64-1 . . . 64-n areturned on by the control circuit in series from the left (64-1) to theright (64-n) illustrated in the FIG. 5A, the drive current from theoutput terminals 63-1 . . . 63-n/2, which are located in the left side,are flowed to the ground line 62 through the switches 64-1 . . . 64-n/2.Then a little part of the drive current flows to the ground through theground terminals 65-2 in the second group, and a large part of the drivecurrent flows on the ground line 62 from the left to the center, andthen flows to the ground through the ground terminals 65-1 of the firstgroup, as illustrated by an arrow in FIG. 5A. On the other hand, thedrive current output from the output terminals 63-(n/2+1) . . . 63-n atthe right side, flows to the ground line 62 through the switches64-(n/2+1) . . . 64-n, respectively. Then a little part of the drivecurrent flows to the ground through the ground terminals 65-3 in thethird group, and a large part of the drive current flows on the groundline 62 from the left to the center, and then flows to the groundthrough the ground terminals 65-1 of the first group, as illustrated byan arrow in FIG. 5A

When a contact resistance value of each of the ground terminals 65-1,65-2 and 65-3 is the same, and is set at the range between 1Ω (min) and10Ω(max), and when the number (m) of the ground terminals 65-2 is set attwenty (20), the number (n) of the ground terminals 65-3 is also set attwenty (20), and the number (l) of the ground terminals 65-1 is set atforty (40), each sum of the contact resistance of the ground terminals65-2 and 65-3 of the second and the third groups would be at the rangebetween 0.1Ω (min) and 0.5Ω(max) and the sum of the contact resistanceof the ground terminals 65-1 of the first group would be at the rangebetween 0.05Ω (min) and 0.25Ω(max). Thus, seventy percent (70%) of thedrive current flows to the ground through the ground terminals 65-1, andthe rest (30%) of the drive current flows to the ground through eitherof the ground terminals 65-2 or 65-3.

According to the second embodiment of the invention, since a pluralityof the ground terminals 65-2 and 65-3 are formed at the both ends of theground line 62 in addition to a plurality of the ground terminals 65-1near the middle of the ground line 62, it could be reduce thedifferences of the power supply impedance, which may occur between thescanning lines COM, each of which is connected to one adjacent scanningline drive circuits. Accordingly the uniformity of displaying the imagesat the scanning lines having a difference of the power supply impedancecan be eliminated.

Furthermore, since a sum of the contact resistance of the groundterminals 65-1 of the first group is smaller than that of both theground terminals 65-2 and the ground terminals 65-3, it could cause alarge part of the drive current to flow to the ground through the groundterminals 65-1 located near the middle of the ground line 62 so thatalmost the same benefit performed in the first embodiment can beexpected.

Moreover, since each of the pitches p1 between the ground terminals 65-1of the first group is set to be greater than each of the pitches p2between the ground terminals 65-2 of the second group or each of thepitches p3 between the ground terminals 65-3 of the third group, degreeof density of the ground terminals 65-1 is higher than that of theground terminals 65-2 or that of the ground terminals 65-3. Thus, thelength of the scanning line drive circuit 60A at its longer side can besuppressed to become further longer. Furthermore, in the secondembodiment of the invention, since the size of the ground terminals65-1, 65-2 and 65-3 are the same, a plurality of the ground terminals65-1 in the first group is formed in order to excess the number (m) or(n) of the ground terminals 65-2 and 65-3. However, a single groundterminal having a planar dimension, which is larger than the totalplanar dimension of either the ground terminals 65-2 or 65-3, may bedisposed near the middle of the ground line, and connects thereto.

While the invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Thus, shapes, size and physical relationship of eachcomponent are roughly illustrated so the scope of the invention shouldnot be construed to be limited to them. Further, to clarify thecomponents of the invention, hatching is partially omitted in thecross-sectional views. Moreover, the numerical description in theembodiment described above is one of the preferred examples in thepreferred embodiment so that the scope of the invention should not beconstrued to limit to them. For example, in the display area 50 of thedisplay panel 40 in the FIG. 50, another circuit consignation can beemployed. In the embodiments, although the organic EL devices are used,other display devices, such as a light emitting diode (LED) can beemployed to both embodiments. Further, the number (l) of the groundterminals 65-1 and the numbers (m) and (n) of the ground terminals 65-2and 65-3 may be set as a desired ratio. Moreover, in the embodiments,although the scanning line drive circuits 60 and 60A are explained forthe sake of brevity, both embodiments can be applied to another displaydrive circuit, such as the data line drive circuit 70. For example, theground line 62 can be replaced with the power supply line, the switches64 can be replace with other switches, each having a differentconfiguration, and the ground terminal 65 can be replaced with an powersupply terminal.

Various other modifications of the illustrated embodiment will beapparent to those skilled in the art on reference to this description.Therefore, the appended claims are intended to cover any suchmodifications or embodiments as fall within the true scope of theinvention.

What is claimed is:
 1. A display system, comprising: a display panel fordisplaying an image, the display panel including a glass substrate; aplurality of lead lines formed on the glass substrate; and a displaydrive circuit for controlling the displaying of the image by the displaypanel, the display drive circuit being formed as a chip and connected tothe lead lines, the display drive circuit comprising: arectangularly-shaped substrate having a main surface and having a longerside that is longer than another side of the rectangularly-shapedsubstrate; a power supply line formed on the main surface of therectangularly-shaped substrate, the power supply line being disposedalong the longer side of the rectangularly-shaped substrate; firstground terminals formed at an end portion of the power supply line; andsecond ground terminals formed at a center portion of the power supplyline.
 2. A display system as claimed in claim 1, the display drivercircuit further comprising: a plurality of switches disposed along thepower supply line, and connected to the power supply line; and aplurality of output terminals formed on the main surface of therectangularly-shaped substrate and connected to the plurality ofswitches.
 3. A display system as claimed in claim 2, wherein an amountof a current flowing in the power supply line to the first groundterminals is smaller than an amount of a current flowing in the powersupply line to the second ground terminals.
 4. A display system asclaimed in claim 1, wherein a size of each terminal of the second groundterminals is the same as that of each terminal of the first groundterminals, and wherein a number of power supply terminals of the secondground terminals is greater than that of the first ground terminals. 5.A display system as claimed in claim 1, wherein each pitch betweenterminals of the second ground terminals is greater than that of thefirst ground terminals.
 6. A display system as claimed in claim 1,wherein the power supply line is a ground line supplying a groundelectric potential, and wherein each of the first and second groundterminals supplies the ground electric potential.
 7. A display system asclaimed in claim 1, wherein a ratio of a length of the power supply lineto a width of the power supply line is 20:1.
 8. A display system asclaimed in claim 1, wherein a total planar dimension of the secondground terminals is set to be larger than a total planar dimension ofthe first ground terminals.
 9. A display system as claimed in claim 1,wherein each of pitches between terminals of the second ground terminalsis set to be greater than each of pitches between terminals of the firstground terminals.
 10. A display driver circuit, comprising: arectangular-shaped substrate having a main surface and having a longerside that is longer than another side of the rectangular-shapedsubstrate; a power supply line formed on the main surface of therectangular-shaped substrate, the power supply line being disposed alongthe longer side of the rectangular-shaped substrate; first groundterminals formed on the main surface of the rectangular-shaped substrateand connected to an end portion of the power supply line; and secondground terminals formed on the main surface of the rectangular-shapedsubstrate and connected to a center portion of the power supply line.11. A display driver circuit as claimed in claim 10, further comprising:a plurality of switches disposed along the power supply line, andconnected to the power supply line; and a plurality of output terminalsformed on the main surface of the rectangularly-shaped substrate andconnected to the plurality of switches.
 12. A display driver circuit asclaimed in claim 11, wherein an amount of a current flowing in the powersupply line to the first ground terminals is smaller than an amount of acurrent flowing in the power supply line to the second ground terminals.13. A display driver circuit as claimed in claim 11, wherein each of thefirst and second ground terminals has a same size, and wherein a numberof the second ground terminals is greater than that of the first groundterminals.
 14. A display system as claimed in claim 1, wherein each ofthe first and second ground terminals has a same size, and wherein anumber of the second ground terminals is greater than that of the firstground terminals.
 15. A display driver circuit as claimed in claim 10,wherein a total planar dimension of the second ground terminals is setto be larger than a total planar dimension of the first groundterminals.